Each of us has our own criteria we use when selecting which camera to buy. Sensor performance, handling, ergonomics, auto-focus, lens selection and other factors can all play a part. Many photographers are very interested in the sensor performance of their cameras, and this short article discusses ISO impact on sensor performance.
NOTE: Click on images to enlarge.
While it is impractical to provide sensor performance details on a wide selection of cameras, this article references DxO test data for a small number of cameras to reinforce a critical fact. Shooting at higher ISO’s has a significant, negative impact on the dynamic range and colour depth performance of a digital camera.
To start, let’s have a look at dynamic range.
The above chart highlights DxO dynamic range test scores for a few different cameras including the Nikon 1 J5 and V2, Panasonic GH4, Olympus E-M1, Nikon D7200, Canon 760D, Sony Alpha 77II, and the Nikon D810. I chose these cameras for a few reasons. The Nikon 1 J5 and V2 are both cameras that I own and use. They also represent examples of different sensor technologies. Each of the other cameras in the chart, whether they have M4/3 sensors (GH4, EM-1), APS-C cropped sensors (D7200, 760D), or full frame (Alpha 77 II, D810), has the highest dynamic range score in its category and/or in its brand based on sensor size.
You’ll notice that as ISO is increased every camera suffers from a loss of dynamic range. DxO suggests that a difference of 0.5EV in dynamic range will be noticeable for most people.
As you compare the sensor performance of various cameras noted in the chart some potentially surprising facts will begin to emerge. For example, the Nikon D810 and D7200 are the dynamic range leaders at base ISO. When shot at even ISO-400 their respective dynamic range performances drop quickly. At ISO-400 they become basically equal to M4/3 cameras like the GH4 and E-M1 when those cameras are shot at ISO-200.
Another interesting comparison is between the J5 and 760D. When shot up to ISO-400 there is no discernible difference in dynamic range, even though there is a significant one in terms of sensor size between the two cameras.
It may be a bit shocking to many folks when examining the data to discover that shooting a Nikon 1 J5 at ISO-200 produces dynamic range performance equal to a D810 when shot at ISO-800.
Now, let’s have a look at the percentage of dynamic range loss when various cameras are shot at common ISO’s such as ISO-400, ISO-800 and ISO-1600.
As you can see in the table above, even moving to ISO-400 causes a D7200, Alpha 77 II and D810 to lose over 10% of their dynamic range. Push that further to ISO-1600 and these same cameras lose 25% or more of their dynamic range.
What is clear is that when we are ‘sloppy shooters’ and use higher ISO’s than necessary it will have a significant, negative impact on the dynamic range performance of the sensor in our cameras and resulting images.
Let’s examine colour depth.
All cameras lose colour depth as they are shot at higher ISO’s. DxO suggests that a difference of 1.0-bits in colour depth is needed to be noticeable for most people. It is interesting to note that the colour depth of a D810 when shot at ISO-400 is similar to that of an E-M1 when shot at ISO-200. A Nikon 1 J5 shot at ISO-200 is similar to that of a D810 when shot at ISO-800.
As we can see in the chart above, all cameras lose a significant percentage of their colour depth as ISO’s are increased from base ISO. This reinforces the notion that regardless of the cameras each of us own, shooting at the lowest possible ISO (given subject matter and allowable lighting) will produce the best quality images.
There are some practical considerations that emerge from examining these data for dynamic range and colour depth. First is the importance of shooting cameras at their base ISO whenever possible to maximize sensor performance. The second is the importance of using a monopod or tripod whenever necessary to help lower the ISO at which an image is captured. And, the third is how critical it is to have good hand-holding technique as this allows a photographer to use slower shutter speeds and potentially lower ISO’s to attain their desired exposure.
Owners of cameras with larger sensors like APS-C and full frame can sometimes have a rather condescending attitude towards owners of smaller format cameras like M4/3, and crow about how much better the sensors in their cameras perform. The caveat of course is whether these same larger sensor camera owners are actually using their gear in a way to maximize sensor performance by always using the lowest ISO’s possible.
Using smaller, lighter gear can result in it being much easier to capture images hand-held at slow shutter speeds when compared to using heavier gear. Based on the weight variances between camera set-ups differences in shutter speeds of 1 or 2 stops are certainly possible. This could mean using lower ISO’s and better dynamic range and colour depth performance.
As we’ve seen in the data above, that difference in ISO could be a great equalizer in terms of actual dynamic range and colour depth sensor performance achieved when shooting with smaller sensor cameras compared to their larger sensor brethren.
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